The present invention relates to differential gear assemblies, and more particularly to retaining a differential pinion gear on a shaft.
An interaxle differential gear assembly allows an output drive axle to rotate at a different speed than an input drive axle. One type of differential assembly transmits torque from the input drive axle to the output drive axle by rotating a case surrounding a pinion gear assembly. This type is known as a "case driven" differential.
Case driven differentials are a distinct class of differentials that transfer torque by rotation of the case surrounding the differential assembly. Torque is transferred to the pinion gear shaft at a portion of the shaft radially outwardly of the pinion gear. The entire torque load is generally carried by the case. With the case driven differential, the pinion gear is generally retained on its shaft by the case, or by a structure in combination with the case.
In the heavy duty environment, a four pinion gear assembly is generally required in order to transmit substantial amounts of torque through a case driven differential. The four pinion gear assembly distributes the torque over the four pinion gears to reduce tooth stress load on the gears. The pinion gears are generally positioned on a cross-shaped shaft and in a meshing arrangement between a pair of side gears.
A "center driven" differential transmits torque directly to the center of a differential assembly, and generally directly rotates the pinion gear shaft, as opposed to rotating a case. With the center driven differential, the entire torque load is generally carried by the pinion gear shaft.
The prior art methods to retain the pinion gears on its shaft for center driven differentials have utilized a case to provide additional support to retain the pinion gears. Additionally, it is known in the art to use a threaded cap which is received upon a threaded shaft, or to use a snap ring to retain a pinion gear to a shaft. Under high loads, however, both methods are inadequate to retain the pinion gear. A case or other structure is therefore required to assist in retaining the pinion gear on the shaft when the pinion gearing is subjected to high loads. This case is undesirable and adds additional material to the differential, increasing both weight and expense. Further, access to the pinion gears for lubrication is limited. Also, the case reduces the space available for the gears, thus limiting the size of the gears.